On the eve of its next big product announcement, Apple is expanding its super-secret research office in Kendall Square. Several commercial realtors tell me that the Cupertino company has leased more than half a floor at One Broadway, an MIT-owned building that also houses Facebook’s small local team, several venture capital firms, and the Cambridge Innovation Center. The new office, about 13,000 square feet on one of the building’s upper floors, is a major expansion for Apple, which currently has a small team on the building’s fifth floor.

The office is home to a special team of researchers focused on improving Siri, Apple’s intelligent personal assistant and knowledge navigator. The team includes members who previously worked for Nuance Communications, whose speech recognition technology used to be licensed by Apple. It also includes former employees of BBN Technologies, Actifio, and Amazon.

Apple was reported late last June to have built a team of speech recognition experts to enhance Siri, particular to give the software a “neural network” boost.

The company continues to hire more researchers for its Siri group, as evidenced by a couple of job listings it posted last month.

Siri is said to feature some improvements in iOS 8, which is expected to power Apple’s next-generation smartphone and first-generation wearable device, reportedly due to be unveiled at Apple’s special media event tomorrow.